This invention relates to an apparatus for detecting the duration of voice.
In order to recognize separately pronounced words or series of words by a pattern matching method or other similar methods, it is required to correctly detect the duration of each voice generated word or a series of words. If a word is pronounced or spoken when the ambient noise is relatively small, for instance, when the S/N ratio is 30 dB or more and a wideband microphone is used to derive a corresponding voice signal, the duration of the voice generated word or series of words can easily be detected by determining the period during which its amplitude and the number of its zero intersections remain above a predetermined value.
When the ambient noise is large or changes at a high rate, however, it is impossible to correctly detect the duration of a voice generated word or series of words, no matter what data-processing has been carried out to determine the proper threshold value. If the threshold value is set relatively small, a noise larger than the threshold value may frequently be generated, and a so-called "addition error" may occur many times. Conversely, if the threshold value is set relatively large, a voice component whose level is lower than the threshold value may fall out, and a so-called "fall-off error" may occur many times. If the non-voice period can be determined, the threshold value can be changed according to the ambient noise level. In general, however, a non-voice period can not be properly determined. It is therefore extremely difficult to correctly detect the duration of an input voice generated word.